Porous article derived from butadienestyrene copolymer latex and polybutadiene latex



POROUS ARTICLE DERIVED FROM BUTADIENE- "STYRENE COPGLYMER LATEX AND POLYBU- TADIENE LATEX Bailey Bennett, Columbus, and George H. McFadden,

'worthington, Ohio, assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware No Drawing. Application July 23, 1953, Serial No. 369,952

5-Claims. (Cll 260- -2.5)

This invention relates to vulcanized latex foam and articles made thereof and 'is' particularly directed to'v'ulcanized foamsand articles therefrom made entirely from synthetic polymers such as butadiene-styrene copolymers andthe" like.

This-application is a continuation-impart of our'copending application Serial No.'203,198, filedDecember 28, 1950' and now-abandoned.

It is, therefore, an object of the invention toprovide -aVulcanizedsynthetic latex foam which has properties approaching vulcanized natural latex foam.

.In carrying out the above object, it isa further object of'theinvention to provide a method for making foamed latex. articles from said foam.

A still further object of the invention is to. provide=a vulcanized foamed latex article andmethod for making .same wherein butadiene-styrene copolymer forms asub .stantial, portion of the article and wherein modifying synthetic latices are added for controlling the physical properties thereof.

"In carrying out the above object, it is a further object of the invention to modify the physical characteristics of an articlefmade of vulcanized foamed butadiene-styrene copolyrn'er latex wherein additions of polybutadiene latex are madeincontrolled quantities, for modifying theresilienceof the articleover a wide range of temperatures.

A still further object ofthe' inventionis to providean article made from vulcanized foamed synthetic latex. specifically a mixture of butadiene-Sty'reriecopolyirier latex and polybutadiene latex, wherein the polybutadiene latex ytpercentagerranges from to 50% of the total latex lnsed.

A still .further object of the invention is to -provide ran article made from vulcanized butadiene-styrene cojpolymer latex and a method of making such an article nvherein the .entire article is made from -a synthetic latex rand wherein the resilience and otherphysical characterisltlCS thereof aremodified so as to appro'achthe physical characteristics of an article .made of vulcanized foamed tadiene-styrene icopolymerlatex are quite satisfactory at elevated temperatures 'lbut when the temperature is decreased, the article loses its resilience and becomes dead to the feellhaving no satisfactory comeback upon compression.

. .IEhis apeculiar phiysical characteristie of "vulcanized foamed butadiene-styrene copolymer latex has retarded atent l ICC its'-use,' since wherever foamed rubber articlesare to be used, they must react properly over a wide range of temperatures.

It is apparent that due to the cost of butadiene-styrehe copolymer latex, it' is one of the most desirable of latices for commercial use. Furthermore, the commercial'production of this type of latex far exceeds the production of any other synthetic latex.

, -ln order to obviate the difficulties experienced with buta- -diene-styrene copolymer latex when foamed and vulcanized, we have found that additions 'of a specific synthetic latex to butadiene-styrene copolymer latex modifies the characteristics of vulcanized foamed latex-articles-made therefrom siifficiently to provide a-satisfactory article for commercial use. Specifically the addition of-polybritadiene latex is proposed in specific quantities in order'to modify the final characteristics of a combination which includes polybutadiene latex and butadine-styrene (fopolymer latex as the entire latex ingredient. The addition of polybutadiene latex markedly increases theresiliency of vulcanizedfoamed latex articles made from the mixture over like articles made from 100% butadienestyrene copolymer latex foam.

We have found'thatadditions varying from 10 to -oft polybutadiene latex (having a solids content of about 45%) to butadiene-styrene copolymer latex (of solids or above) produce a latex which, when compounded,

foamed and cured, provides an article that has increasing resilience in proportion to the quantities ofp'olybutadiene latex used.

in practice we have found that any of the commercial butadiene-styrene copolymer latices are satisfactory for use in thepr ocess to be described hereinafter. Such latices asLotol '50l0 C'( obtainable from the U. 5. Rubber Company, Naug'atuclc Division), GRStype 4 (50% buta- "die'ne-50'% styrene, 50 to solids) or any other butadiene Styren'e copolymer latex, which will meet the requirements hereinafter set forth, will provide satisfactory results.

Properties of LotolSOlO-C are as follows:

Total solids concentration. 55.0% minimum. Hydrogen ion concentration 10. 51l.0.

(P Particle size and charge Approx. 0.15 micronnegative. Styrene inpolymer Approx. 455

"Mooney viscosity of poly- -100.

Gas type4'is also known as Polysa'rS latex 4 Canada) and is an equivalent 'ofa heatconcentrated X230 latex cases, it is desirable, though not essential, to have a reasonably high "solids content since one -ieijuirenient Whichmust be adhered to is the final solids content of th'e combined laticeswhich must be 50% or more. Thus,

if the -butadiene styrene'copolymer latex havinga solids cb'ntent of 55% is utilized, it is necessary that the poly: butadie'ne latexhas a solids content of at least 45%, if a 50-50 mixture-is robe used. On the other hand,"if a butadiene-styrene copolymer latex, 10% polymtadiene latex mixture is used 'it is "obvious that thesolids in the polybutadiene latex may bernuch lower than '45 for example, polybutadiene from Recipe #3, may be used wherein 10% polybutadiene having a solids content nr pranmael together "with 90% or biitadiene- *st yrenecopolyih'er latex having asolids content of 55 Similarly, 38 solids polybutadiene may be used in quantities .of 20% with 80% butadiene-styrene copolymer latex having a solids content of 55%. In each case, the

total solids content of the mixture will be above 50% which is one of the requirements of this invention.

It is further apparent that high solids polybutadiene latices (as made by usual concentration processes) may be used wherein the solids content ranges up to 56%. In

- this case, 30% of polybutadiene latex having a 56% solids content may be mixed with 70% of a butadiene-styrene copolymer latex having a solids content of 55%.

yields a final product having 55+% solids.

In general, however, a relatively high solids content in the polybutadiene latex is desirable, although not neces- :sarily controlling so long as the final solids in the latex rmixture used for compounding and foaming is 50% or more. To illustrate the wide variation in polymerization r ingredients which may be used to make the polybutadiene 'Jlatex the following recipes are given, which recipes are -rused in emulsion polymerization processes to form a polyibutadiene latex in which the contained polymer has a viscosity average molecular weight of about 400,000 to -.500,000 as distinguished from the syrupy type of poly- -mers whose molecular weight is generally below 100,000. This viscosity may be measured with an Oswald type p H of water phase adjusted to 10.5 with sodium hydroxide. Polymerization time about hours. Polymerization temperature, 50 C.

Solids content, 48.6%.

Recipe #2 (All parts by weight) Parts Water 2.. 85.0 Sodium stearate 2.15 Potassium persulfate 0.15 t-Dodecyl mercaptan .c 0.2 Butadiene 50.0

Latex alkaline, preferably above 9.8. Polymerization time, 40 hours. Polymerization temperature, 50 C. ,Solids content, 38%.

Recipe #3 All parts by weight) Parts Water 90.0 Potassium oleate 2.15 Potassium persulfate 0.2 Potassium ferricyanide 0.1 "Sodium hydroxide 0.04 .It-Dodecyl mercaptan 0.2 ,Butadiene a 50.0

pH of latex, 11.

Polymerization-time, hours.

Polymerization temperature, 50* C.

:S'olids' content; 26%. 1

The polymerization temperature of 50 C. appears to negpf, most satisfactory temperatures for the reac- This tion, although satisfactory latices have been made at temperatures as low as 5 C. and this figure is in no way critical but may vary according to the conditions of polymerization and time consumed during the reaction.

The butadiene-styrene copolymer latex may vary over wide ranges of butadiene-styrene percentages in the initial reaction mixture although commercial charge ratios utilize styrene from 5 to 50% and any latex made within these limits will be satisfactory. It is obvious that the resilience figures to be noted hereinafter will vary with the percentages of styrene and butadiene-styrene copolymer, all of the figures listed here having been obtained utilizing a Lotol 50l0-C latex which is readily available in commercial grades. However, in every case the resilience of the mixture will be a definite improvement of the butadiene-styrene copolymer alone.

, In the compounding of vulcanizable latex foams, the following ingredients are used:

In the above recipe the use of glass fiber may vary or may be omitted, particular advantage of said use being set forth in Patent #2,498,785, assigned to the assignee here. Instead of pHR any satisfactory bulfer may be used which will adjust the pH of the mixture within the desired range. In place of sodium fluotitanate other fluotitanates as noted in Patent #2,472,054, or fluozirconates as noted in Patent #2,472,055, may be used or bility control, all of these variations being well known.

The master batch as noted in Recipe #4 hereinafter set forth may vary Widely, the specific formula being given merely to set forth the conditions under which the test samples hereinafter noted were made.

Recipe #4 Parts by weight Zinc oxide.. 600 Titanium oxide 120 Sulphur 300 Zinc mercaptobenzothiazole 150 Piperidinium pentamethylene dithiocarbamate Zinc diethyl dithiocarbamate .s...... 60 Symmetrical dibetanaphthyl-p-phenylenediamine 90 Ammoniacal casein solution (10%) 525 Darvan #1, 10% solution (sodium salt of polyalkyl aryl sulfonic acid) 358 In each case, the foam was brought to a satisfactory height, was filled into a mold, gelled, cured in open steam COMPOSITION Percent Percent Lotol Polybuta- Rwllienoy dlene lThe polybutadiene in the above table is the type'lnado by :Recipe #l andtincludes-about 48% solids, while the Lotol is the 50l0-C type.

Inall cases, the test samples were approximately 14x 14 x 3.6 cm. and the densities were substantially constant.

All resiliency figures are .Bashore. resiliometer readings ..silience wasii improved .over a l% .butadiene-styrene ccpolymer latex test sample.

In order to demonstrate the increase in resilience over a wide range of temperatures, the following figures are given, the resilience test being conducted identically to those noted heretofore and with the same test samples:

COMPOSITION [Tests at 15 C. (59 F.).]

Percent Percent Lotol Polybuta- Resiliency dlenc [Tests at 82 C. (179.6 F.).]

Percent Percent Lotol Polybuta- Resiliency diene 100 sss ssssss 38. 4 90 10 38. 6 B0 20 38. S 70 30 41. 0 00 40 43. 0 50 50 48. t

The polybutadiene used in this series of tests was made by Recipe #1 and includes about 48% solids. The Lotol is the 5010-C type.

It will be noted from the results of these tests that the resiliency of a wide range of temperatures is markedly improved by the addition of polybutadiene latex and that the resilience of vulcanized synthetic foamed latex articles is most improved when 30% to 50% of polybutadiene latex is added to a butadiene-styrene copolymer latex.

The results of four different compositions are noted hereinafter wherein physical characteristics are listed:

Percent Percent Tensile Elongation, Modulus Lotol Polybu- Shore A (p. s. 1.) Percent (p s. 1. at

tadiene 300 All test slabs compounded and cured under identical con ditions. The polybutadiene used in this series of tests was made by Recipe #1 and includes about 48% solids. The Lotol is the 50l0-C type.

From the figures listed above it will be noted that at the greatest resiliency, namely a 50-50 mixture, that the tensile strength is still satisfactory for cushion material while the elongation has not changed markedly, although somewhat reduced, and the modulus at 300% elongation has dropped off slightly. It will be noted in all cases that the Shore A hardness is substantially constant. In the above tests all samples were tested in accordance with standard AJS. TQM.- rnethods for tension testing of 'vulcanized rubber.

In all cases butadiene-styrene 'copolymer latexjforms the basic ingredient of the latex mixture due to the'fact that evenwith SO-SOlatexmixture the solids content of the butadiene-styrene copolyrner latex is preferably above 50% while the solids content of the polybutadiene latex is preferably below 50%.

From the aforegoing, fifty percent polybutadiene latex addition to butadiene-styrene copolymer latex is the prefered maximum addition. In this respect, it is tobe observed that as the resiliency of the composition is improved, the tensile strength thereof is reduced. For this reason itis necessary to utilize a composition wherein the resiliency is at the most desirable figure compatible with other physical characteristics of the article. In other words, a balance between the resiliency and other phy sical characteristics forms the basis for the limtis of the polybutadiene addition. It has been found that tensile strength drops off as the percentage of polybutadiene increases; that elongation drops olf slightly and that the modulus at 300% elongation decreases slowly. Thus, with the exception of the resilience, the remaining physical characteristics of the composition foam are decreased, whereby it is necessary to choose a maximum, addition figure which yields satisfactory physical characteristics to gether with a useful resiliency.

While the embodiment of the present invention as here in disclosed, constitutes a prefered form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In a method of controlling the physical characteristics of the resilient foamed latex articles made from compounded, foamed and vulcanized synthetic latex wherein a rubbery butadiene-styrene copolymer latex including at least 50% solids therein is the basic latex ingredient, the step comprising, mixing therewith p-olybutadiene latex in which the contained polymer has a molecular weight of about 400,000 to 500,000 in percentages of 10 to 50% of the total weight latex to be foamed, said polybutadiene latex having a solids content sufiicient to bring the solids content of the mixed latex to at least 50% by weight whereby the resilience of the article is markedly improved.

2. in a method of controlling the physical characteristics of the resilient foamed latex articles made from compounded, foamed and vulcanized synthetic latex wherein a rubbery butadiene-styrene copolymer latex having a solids content of about 55% by weight is the basic ingredient, the step comprising, mixing polybutadiene latex in which the contained polymer has a molecular weight about 400,000 to 500,000 and a solids content of between 45 and 49% by weight of the total latex to be foamed whereby the solids content of the mixed latex is maintained to at least 50% whereby the resilience of the article is markedly improved.

3. In a method of controlling the resilience of articles made essentially from rubbery butadiene-styrene copolymer latices having solids contents of 50% and above wherein the latex is compounded, foamed and vulcanized, the step of modifying the resilience of the vulcanized article by polybutadiene latex additions to the butadienestyrene copolymer latex in the initial mixture of latices to be foamed wherein the contained polymer in said polybutadiene latex has a molecular weight about 400,000 to 500,000 and wherein the total latex mixture is of an alkaline character and has a solids content of at least 50% by weight and wherein the butadiene-styrene copolymer latex makes up the major ingredient of latex by Weight and within the range of 50 to by weight of the mixture.

4. In a method of controlling the resilience of articles made essentially from rubbery butadiene-styrene copolymer latex wherein the latex is compounded, foamed and vulcanized, the step of modifying the resilience of the vulcanized article by adding polybutadiene latex in quantitles of 10 to 50% by weight in which the contained polymer has a molecular weight about 400,000 to 500,000

v and a solids content above 45% and below 50% by weight tained polymer has a molecular weight about 400,000 to 500,000 in proportions of 10 to 5% by weight and'wherein the entire mixed latex ingredient-hasa solids content of at least 50% by weight.

References Cited in the file of this patent UNITED STATES PATENTS 2,484,434 Van Buskirk et a1 Oct. 11, 1949 2,512,697 Te Grotenhuis June 27, 1950 2,560,031 Cline July 10, 1951 FOREIGN PATENTS 492,998 Great Britain ..Sept. 30, 1938 

1. IN A METHOD OF CONTROLLING THE PHYSICAL CHARACTERISTICS OF THE RESULTANT FOAMED LATEX ARTICLES MADE FROM COMPOUNDED, FOAMED AND VULCANIZED SYNTHERTIC LATEX WHEREIN A RUBBERY BUTADIENE-STYRENE COPOLYMER LATEX INCLUDING AT LEAST 50% SOLIDS THEREIN IS THE BASIC LATEX INGREDIENT, THE STEP COMPRISING, MIXING THEREWITH POLYBUTADIENE LATEX IN WHICH THE CONTAINED POLYMER HAS A MOLECULAR WEIGHT OF ABOUT 400,000 TO 500,000 IN PERCENTAGES OF 10 TO 50% OF THE TOTAL WEIGHT LATEX TO BE FOAMED, SAID POLYBUTADIENE LATEX HAVING A SOLIDS CONTENT SUFFICIENT TO BRING THE SOLIDS CONTENT OF THE MIXED LATEX TO AT LEAST 50% BY WEIGHT WHEREBY THE RESILIENCE OF THE ARTICLE IS MARKEDLY IMPROVED. 